A fundamental problem arising when operating unmanned aerial vehicles (UAVs) is how to avoid mid-air collisions autonomously using on-board sensors. Today, depending on the type of airspace and aircraft, manned aircraft either resort to automatic transponder-based collision avoidance systems like TCAS (commercial airliners), or the pilot's eyes for smaller aircraft using Visual Flight Rules (VFR). Operating UAVs today usually require segregated airspace keeping out from civilian air traffic. The next generation UAVs need to be able to fly autonomously in civilian air space and therefore also need an autonomous collision avoidance system that detects both transponder-based vehicles as well as other aircraft without transponders (parachuters, gliders, other UAVs, etc).
Manned aircraft flying in controlled airspace maintain a safe distance between each other using the service provided by an Air Traffic Control (ATC). ATC informs and orders human pilots to perform manoeuvres in order to avoid Near-MidAir Collisions (NMAC). The last decade semi-automatic systems like ACAS (Airborne Collision Avoidance System) have been implemented that essentially moves this responsibility from ATC to the pilot. ICAO (International Civil Aviation Organization) stipulates that all manned aircraft with more than 19 passengers carry an ACAS system. The present implementation of ACAS (called TCAS II) gives the pilot a warning (e.g. “climb, climb”) and a so called Resolution Advice (RA) when the risk of collision between two aircraft exceeds a certain threshold. The pilot then performs the recommended manoeuvre manually. A transponder based link ensures that the RA given to the pilots on both aircraft is such that the best manoeuvre is taken jointly to avoid a collision.
The ACAS/TCAS system, however, assumes that both aircraft exchanges data on speed, height and bearing over a data link and that both systems cooperate. When operating small UAVs this assumption is often no longer valid. A typical UAV operates on altitudes where small intruding aircraft are often present that do not carry transponders. This paper describes a method for detecting hazardous situations based on data from a passive bearings-only sensor.
One of the most important dichotomies is the choice of state vector propagation: Nominal, worst-case or probabilistic. The probabilistic approach provides a framework that allows combining the naturally occurring uncertainties in measurements in a stringent framework.
A challenge with bearings-only measuring sensors is how to deal with the significant uncertainty obtained in estimated relative distance. One approach to increase accuracy in the distance estimate is to perform own platform manoeuvres.
In Monte-Carlo methods the probabilities are calculated for multiple points of an uncertain area around the detected object. Monte Carlo methods are known to be able to approximate probabilities arbitrarily well. They are also known to be computer intensive particularly when the underlying probabilities are small.
The object of the invention is to provide a method to compute a probability of near midair collision between two vehicles/objects that may be performed on a vehicle in real time.